The light-emitting diode (LED) army is widely used in the heads of printers or photocopy machines. As shown in FIG. 1, a typical printer head with LEDs comprises an optical lens 71, for focusing the light from the LEDs, and a light source area 72, equipped with LED array components and optical components, for emitting light to penetrate the optical lens 71 and project unto the corresponding location on the photo conductor drum 70 of the printer. The projection, combined with the subsequent operations constitutes the printing of the desired patterns.
FIG. 2 shows a schematic diagram of a conventional structure using LED as light source. The structure comprises a printed circuit board (PCB) 81, a plurality of LED chip arrays 82, arranged end-to-end to cover the entire length of the printer head, and installed on the surface of the PCB 81, and a plurality of driving devices 83, arranged in a line parallel to the LED chip arrays, and also installed on the surface of the PCB 81. The wire bonding 84 is used to electrically connect the driving devices 83 and the LED chip arrays 82, and the wire bonding 85 is to electrically connect the driving devices 83 to the conductive pattern on the PCB 81 to generate the required light source. However, there are several drawbacks in manufacturing the above structure:                1. Low yield rate: In the LED chip arrays 82, the individual LED has a small light emitting area, and the component density is high. For example, for a resolution of 600 dpi, it requires a light emitting area with 5000 LEDs. Furthermore, it also needs to wire bond from the bond pad on the LED chip arrays 82. That is, it needs to wire 5000 times in order to complete the 5000 wire bonding 84. Under such circumstances, because of the large number of wires and their high density and accuracy, and the difficulty of fixing a plurality of LED chip arrays 82 on the PCB 81, it is difficult to control the precision. Therefore, the yield rate of the manufacturing is usually low.        2. High production cost: The test can only begin after the above structure is complete, that is, after 5000 wiring. If there is any defect, it is difficult to replace the defect components since they are densely arranged. In this case, most products with any defects will be thrown away. Therefore, the average production cost is high.        3. High investment cost: Because the LED chip arrays must be aligned precisely along the same axis, it requires a high precision equipment, which means a higher investment cost.In summary, the unit cost of the product is high because it is hard to alleviate the above three drawbacks.        